The present invention is directed to an actuator of a type usable for making positional adjustments in technical or scientific instruments including interferometers and space-based or other telescopes.
In a number of situations, it is useful to make both coarse and very fine changes or adjustments in position such as by an actuator. One area in which such positional adjustments may be useful is for adjustment, calibration, pointing, focusing and the like, of various technical or scientific instruments including interferometers and telescopes, particularly space-based telescopes and wireless communications components, e.g., antennas and other types of signal receptors. In the case of telescopes, the fineness or precision with which mirrors, mirror segments or other optical components must be positioned may be substantially finer than the step size with which an actuator, in a particular application, may be moved. Although actuators are of various types and are available with a variety of step sizes or precisions, there are often other constraints limiting the types of actuators available, including constraints on the size, weight, cost, suitable environment, or other performance characteristics of an actuator. Accordingly, in many situations, it is desired to use an actuator which has movement components or steps of a given minimum size but to achieve positioning of a telescope mirror segment or other optic with a precision which is finer than that of the actuator. These problems can be particularly acute in the case of a space-based telescope because of the tight constraints which weight and reliability place on actuator components. Accordingly, it would be useful to provide an actuator suitable for technical or scientific instruments, preferably suitable for a space-based telescope or other instruments.
In some actuators, the degree of fineness of adjustment is achieved at the price of an unacceptable reduction in the range of motion of the device. In some devices it was difficult or impossible to provide for the necessary coarse adjustment in addition to the necessary fine adjustment. Accordingly, it would be useful to provide an actuator which provides a relatively fine adjustment throughout a relatively large range of motion, preferably with a substantially predictable reduction ratio, and/or which allows for coarse adjustment as well as fine adjustment of position.
In space vehicles, size, weight, and power limitations are of paramount importance. For example, scientific or technical instruments and related components, such as actuators, on board such vehicles typically must have a low mass, small size, and low power consumption. In particular, actuators often must be capable of carrying heavy loads (i.e., have high strengths) due to the severe stresses caused by the vehicle velocities and accelerations and vibrations experienced during launch and/or orbit of the vehicle around a celestial body. Accordingly, there is a need for an actuator that is capable of providing all of the capabilities necessary (e.g., broad positioning range and resolution, low mass, small size, high degree of stiffness, high load capability, wide operating temperature range, low power consumption, etc.) for the positioning applications required by today""s market but at a reasonable cost.
According to a first aspect of the present invention, a reduction device or fine positioning system is provided that provides at least certain motions using flexures. In one embodiment, left and right sidewalls are provided with intermediate flexures allowing them to be configured in a slightly angular or xe2x80x9cVxe2x80x9d shaped fashion, e.g. by moving the flexures of the left and right sidewalls farther apart or closer together. The upper and lower edges of the left and right side walls are joined, preferably also by flexures, to upper and lower walls which move together or apart as the sidewall intermediate flexures are moved farther apart or closer together. In one embodiment the distance between the sidewall intermediate flexures is adjusted by deflecting a member, such as a plate, rod or bar extending between the left and right intermediate flexures. For example, by coupling the output end of a linear actuator (such as a lead screw-type actuator) to the middle region of the deflectable member, extending the actuator will deflect the mid-portion of the member upward, pulling the end points, and thus the coupled left and right intermediate flexures, closer together. The amount which the upper wall moves (relative to the lower wall) in response to a given movement of the actuator can be configured by selecting or adjusting the angles defined by the intermediate, upper and lower flexures of each sidewall and/or the manner in which the actuator is (directly or indirectly) coupled to the left and right intermediate flexures. Because certain portions are provided with relative movement by flexures (as opposed to, for example, hinges), portions which move relative to one another can be provided as regions of a single integral part, without the need for or use of joints between separate parts. Such a single integral piece is thus more easily maintained at a substantially uniform temperature and the potential for failure of hinges or other couplings between separate parts is reduced or eliminated.
In another embodiment, the fine positioning system includes: (a) a flexure member including an upper wall, a lowers wall and at least two sidewalls coupling the upper and lower walls; and (b) a linkage configured to change the distance between the intermediate flexure joints of the two or more sidewalls in response to movement, particularly rotational movement, of a motor shaft. Each sidewall is movably coupled to the upper wall at a flexure joint defining upper flexure axes and to the lower wall at a flexure joint defining lower flexure axes, and has an intermediate flexure joint to accommodate positive and negative vertical movement of the upper wall with respect to the lower wall. The linkage includes a flexure member having at least one flexure joint defining a flexure axis and a displacement controlling member engaging the flexure member. The displacement controlling member is coupled to the motor shaft and includes at least one flexure joint defining an oscillatory flexure axis that is offset or distinct from the flexure axis of the flexure member. Typically, the oscillatory flexure axis is transverse to the flexure axis of the flexure member. In one configuration, the oscillatory flexure axis permits horizontal and vertical displacement of the displacement controlling member while imparting vertical displacement only to any portion of the flexure member.
In another configuration, the linkage includes a cam, or device for displacing the displacement controlling member in transverse first and second directions. The displacement controlling member is configured to displace at least a portion of the flexure member about the member""s flexure joint in the first direction and dampen the movement of the at least a portion of the flexure member in other directions.
In one configuration, the structure includes left, right, front and rear sidewalls coupling the upper and lower walls. Each sidewall is movably coupled to the upper wall at a flexure joint defining upper flexure axes and to the lower wall at a flexure joint defining lower flexure axes. Each sidewall has an intermediate flexure joint to accommodate movement of the upper wall with respect to the lower wall.
Flexures, as described herein, are believed particularly useful in operation at cryogenic temperatures, especially when formed of suitable cryogenic materials such as titanium alloys, beryllium and the like. The relatively strong flexure structure that can be achieved in this fashion not only provides a component better able to withstand launch acceleration and vibrations or other stresses, but offers a potential for a component which acts both as a support for a mirror (or other optical component) and an actuator (rather than requiring separate actuator and mirror support).
According to a second aspect of the present invention, a positioning device, e.g., actuator, is provided that is capable of performing both fine and coarse adjustments in a highly efficient manner. The device is particularly useful for adjusting the position of optical and communications components, especially in cryogenic or space applications. The device includes a fine positioning system for fine displacements of the object in a desired direction (e.g., a fine positioning means for displacing the object to a target position); a coarse positioning system for coarse displacements of the object in the desired direction (e.g., coarse positioning means for displacing the object to a coarse position approximating the target position); a motor having a shaft engaging the fine and coarse positioning systems; and a coupling (or coupling means) for selectively engaging and disengaging the coarse positioning system from the shaft. In this manner, a common motor is capable of operating both the fine and coarse positioning systems.
The fine and coarse positioning systems can be of any gear driven configuration as will be evident to those of ordinary skill in the art. In a preferred configuration, the fine positioning system is the flexure structure described above and the coarse positioning system includes a threaded coarse positioning shaft engaging the motor shaft by means of a plurality of interlocking gears. The threaded coarse positioning shaft is received in a threaded nut that is fixedly attached to a support surface. As the threaded coarse positioning shaft is rotated clockwise or counterclockwise, depending on the direction of turning of the threads, the shaft is elevated or lowered relative to the threaded nut, thereby elevating or lowering the attached object.
In one configuration, the coupling includes a pair of opposing gears. Each of the opposing gears has or is engaged with a locking member configured such that, in a first mode when the locking members are disengaged from one another, the opposing gears are independently rotatable in forward (e.g., clockwise) and reverse (e.g., counterclockwise) directions and in a second mode when the locking members are engaged with one another, the opposing gears are not independently rotatable from one another in at least one of the forward (e.g., clockwise) and reverse (e.g., counterclockwise) directions. In the first mode, the fine positioning system is able to make positive or negative adjustments to the position produced by the coarse positioning system without movement of the coarse positioning system.
In another embodiment, a method for positioning an object is provided. The method includes the steps of:
(a) rotating a motor shaft in a forward (e.g., clockwise or counterclockwise)direction to displace the object to a coarse position approximating a target position; and
(b) rotating a motor shaft in a reverse (e.g., counterclockwise or clockwise, respectively) direction opposite the forward direction to disengage a coarse positioning member from the motor shaft and to displace the object to the target position using a fine positioning member engaging the motor shaft.
In one process configuration, during the rotating step (a) both the fine and coarse positioning members displace the object.
In another process configuration, rotating step (b) includes the substeps of:
(i) rotating a cam to displace a displacement controlling member in first and second directions, wherein the first and second directions are transverse to one another;
(ii) displacing at least a portion of a flexure member in the first direction with substantially no displacement of the at least a portion of the flexure member in the second direction; and
(iii) displacing at least two sidewalls of a flexure structure either inwardly or outwardly, thereby causing an end surface of the structure to be displaced in the first direction.
The present invention thus provides a structure which is usable in connection with technical, scientific (e.g. astronomical) or other instrumentation to achieve fine position adjustments in a manner which is practical for space-based telescopes or other technical or scientific instruments.